This invention relates to an apparatus for various tasks for semiconductor devices using a focused ion beam such as fabrication of the semiconductor device, exposure, analysis, film formation, and so forth. More particularly, the present invention relates to an ion beam apparatus which makes it easy to set the radiating position when an ion beam is radiated to the lower layer portion of a semiconductor device.
A conventional apparatus for working a semiconductor device using a focused ion beam is disclosed in U.S. patent application Ser. No. 427,584, now U.S. Pat. No. 4,503,329 and EPC Laid-Open No. 0075949, and has the following construction. As shown in FIG. 1 of the accompanying drawings, a beam 10 which is extracted from an ion source 1 while being controlled by an ion source controller 12 is condensed by an electrostatic lens 2 which is in turn controlled by a lens controller 13. The beam 10 is then scanned two-dimensionally on a predetermined region on a target 4 held on an XY stage 5, by a deflector which scans the beam with a scanning signal from a deflector controller 15. The secondary electrons 11 generated from the target 4 are detected by a detector 6, and a luminance modulation signal corresponding to the number of secondary electrons 11 is applied to CRT 14 to provide a scanning ion microscopic image on the basis of the same principle as a scanning electron microscope (SEM). The work position is set while observing the surface of the target 4 with the scanning ion microscopic image.
The XY stage 5 which holds the target 4 is controlled by a stage controller 16. A vacuum chamber 18 is held at a vacuum of at least l.times.10.sup.-6 Torr by a vacuum pump 9. A stool 7 which supports the vacuum chamber 18 as a whole is put on an air support 8 to dampen vibration of the system as a whole.
In accordance with this apparatus, a positioning accuracy of .+-.0.2 .mu.m can be obtained when, for example, an ion beam of gallium (Ga) is focused in a 0.1 .mu.m.phi. to cut a 1 .mu.m wide Al wiring. The workpiece to be worked by this apparatus is a semiconductor device, an exposure mask, or the like.
The section of this semiconductor device consists, for example, of an Si substrate 19, SiO.sub.2 20, an Al wiring 21, an inter-layer insulating film 22, an Al wiring 23, an inter-layer insulating film 24, an Al wiring 25 and a passivation film 26 from the lowermost layer in order named, as shown in FIG. 2.
The flatness of the insulating film 22 on the lowermost Al wiring 21 has been so improved in the past that the information on the lowermost Al wiring 21 can not be obtained by a scanning ion microscope for observing the corrugation on the surface. The information on the second Al wiring layer 23 can be obtained because the insulating film 24 on the second Al wiring 23 has not been made flat. Therefore, positioning the work can be done for the uppermost layer 26 and the second wiring 23 with the scanning ion microscope. However, since film becomes increasingly flatter, there is a strong possibility that the observation can be made only for the uppermost Al wiring 25. This will makes it difficult to locate the work positions of the lowermost Al wirings 23 and 21.
In the semiconductor device shown in FIG. 2, it is possible to observe the layers down to the lowermost Al wiring 21 with an optical microscope because the insulating films are optically transparent. Therefore, the Al wiring 21 can also be worked if the observation is first made with an optical microscope and positioning the work is then effected by a scanning ion microscope. As disclosed, for example, in U.S. Pat. No. 4,447,731 and Japanese Utility Model Publication No. 10687/1984, a conventional combination of the optical microscope with an optical observation instrument does not use an optical microscope to position the work, but is used merely for rough setting of the observation position. The magnification of the optical microscope is low, the optical axis of the optical microscope deviates from that of the optical observation instrument by 100 .mu.m, so that no device is adequate for setting the work position in actual practice.